Horse Power (HP): What is this contact rating?

August 21, 2018
Employee Spotlight

When I think of horse power (HP), I soon think of the many times Tim “the Toolman” Taylor attempts to soup up whatever power tool was featured on his “Tool Time” episode. Things quickly got out of hand (sometimes literally!) as Tim tried to demonstrate his belt sander knowledge. Going along with the theme of explaining some of the contact ratings seen on RIB datasheets, this time I want to cover HP and the associated ratings on our datasheets.

HP is like any other unit of power, which is a way to represent a rate at which work is being done. Power represented in watts (W) is closely related to HP. With great power comes great responsibility – responsibility to choose a correctly rated relay! This chart, found from a Google search of “electric motor horsepower,” helps to convey the electrical current that is consumed at each HP rating. What’s not displayed is the instance of current consumed if the electrical motor happens to be locked, which results in a very high consumption of electrical current.

The HP ratings listed on the 10A, 20A, and 30A rated relays (seen below, respectively) are proven by the UL testing that is performed on the RIB relay devices. With those listed ratings, it is important to notice the specific voltages that are stated. Could our relays handle a 1 HP motor @ 240Vac? Perhaps it could, but we cannot guarantee how long the relay will last. With the listed specifications, the RIB relay devices are guaranteed to last a long life of switching the motor load on and off.

Another important note is that these HP ratings are for conventional AC powered motors. Electronically Commutated Motor (ECM) units do not behave – electrically speaking – like a conventional AC powered motor. UL has not yet made standard specifications for ECM units because of manufacturers have different ways of making a motor into an ECM unit. For a more reliable contact rating for ECM units, look at the “electronic ballast” rating.

So, there you have it – a brief overview of the HP ratings that we have listed on our RIB relay datasheets. I hope this helps you to make a more informed decision of relay size for your next controls project. Of course, please call in and ask for support or email support@functionaldevices.com if you would like a second opinion – we engineers are standing by 8am-5pm EST!

Oh, and did you hear about the man who was hospitalized with six plastic horses inside him? The doctor described his condition as stable.


Author Image

About the Author

Meet Samuel Klennert – you can call him Sam. He was born and raised amongst the farmland of Indiana, which included corn, soybeans, and sometimes wheat. Sam graduated from Purdue University with a Bachelors degree in Electrical and Computer Engineering Technology in 2015. He has a focus in analog circuitry and power electronics, but he’ll give software a try from time to time – just not that digital witchcraft!

Outside of work, Sam enjoys outdoor activities including (but not limited to) hiking, mountain biking (or just really-big-hill biking), and camping. Call Sam for tech support today – he’ll give his best effort to any task at hand!